Power transmissions of the automatic shifting type have a plurality of selectively establishable gear ratios between the engine and ground engaging mechanism for the vehicle. The ratios are generally established by hydraulically operated friction devices such as clutches and brakes. The engagement and disengagement of these devices is controlled by valve mechanisms which direct hydraulic fluid to and from the operating piston of the respective devices. The valve mechanisms have been controlled between upshifted and downshifted positions by control pressure and springs. The control pressure can be established by mechanical mechanisms such as governors and throttle valves or by electrical elements such as solenoids.